In the prior art, there is known an image generating system which can generate an image viewable from a given viewpoint in an object space that is a virtual three-dimensional space. Such an image generating system is very popular as a system which can realize a so-called virtual reality. If the image generating system is for a racing game, a player can enjoy a three-dimensional game by controlling and running a racing car (or object) in the object space to compete with the other racing cars controlled by the other players or computer.
However, an image generated by the prior art image generating system will not be focused depending on the distance from a viewpoint as in the actual human view. Thus, the representation is such that all the subjects within the image are in focus.
The image in which all the subjects ranging between the short distance and the long distance are in focus is abnormal in our daily life.
To pursue the reality, it is desirable that an image is generated in which a focus is regulated depending on the distance between the viewpoint and an object or the direction of sight line. However, the processing load will be increased if a defocused image is generated by calculating the distance between an individual object and the viewpoint within a game space to process the degree of defocusing for each object.
In an image generating system which must generate an image corresponding to a real-time variable viewpoint using its limited hardware resource, it is important that a focused image as in the actual world can be generated using less processing load.